Suggestion: Flags
This might sound weird but here me out, we have pride flags in the game and I think it would be a cool story telling detail to have a recolor of them for the worlds. I live in a university town on the border, everywhere you go in my city there are flags on houses/apartment windows of where the inhabitants are originally from (Mexico/Argentina/Canada/etc).
I think it would be cool for a Sim who grew up in Sulani and moves away to be able to have a flag of Sulani on their dorm room wall. We already have a logo for each world and we already have a flag item so I don't think it would be too hard to recolor the pride flag into world flags. It would be like having state/country flags IRL, I just think it would be a fun detail to add.
Just to clarify, I'm not saying replace the pride flag/add new swatches, I want a recolor of it where each swatch is a different world. It could be base game and include all the Sims worlds in the game (including expansions) so even if you don't necessarily own those worlds you could still tell the story of a Sim being from there, like how we have penpals from Sims 3 worlds.